A known problem in the oil and gas industry is the existence and/or development of fractures in a subterranean formation. Fractures in a formation may cause a number of problems at various stages of the exploitation of a formation, e.g. loss of drilling fluid during drilling, loss of injection fluid during Water Flooding or Enhanced Oil Recovery, or the like.
In order to optimise exploitation of the reservoir, it may be desirable or necessary to treat the fractured formation or “thief zone”, e.g. by completely or at least partially plugging such fractures. Complete or at least partial plugging of the fractures is typically carried out by injecting a cement composition into the fractured formation. This process is commonly known as conformance control.
Conventional conformance treatment of a fractured formation typically follows a trial and error approach, involving pumping multiple batches of cement until the fracture is plugged. However, such an approach is highly inefficient.
U.S. Pat. No. 7,314,082 (Sweatman et al.) discloses a method of improving the pressure containment integrity of a wellbore, the method including pumping a fracture sealing composition into the wellbore. In order to estimate the pressure containment integrity improvement, equations based on an assumed fracture geometry describing the width profile of a fracture are used.
U.S. Pat. No. 8,401,795 (Kaageson-Loe et al.) discloses a method for identifying a risk zone in a segment of a planned wellbore, and selecting a solution to reduce fluid loss in the risk zone.
Published paper SPE 160967, 2012, “Fracture Growth Monitoring in Polymer Injectors-Field Examples” (Khalfan Shuaili et al.) discloses surveillance methods which are used to identify the existence and properties of fractures in polymer injectors. Pressure fall off tests used to determine fracture dimensions in polymer injectors have particular characteristics since they are influenced by shear-dependent viscosity seen in non-Newtonian fluids.
Published paper SPE 99462, 2006, “correlating Gel Rheology With Behaviour During Extrusion Through Fractures” (Wang and Seright) discloses methods using rheology measurements for assessing gel properties in fractures.